Therapeutic proteins provide unique treatments for numerous human diseases and disorders including cancer, multiple sclerosis, hemophilia, rheumatoid arthritis, Crohn's disease and diabetes. Unfortunately, in significant fractions of patients receiving therapeutic protein products (up to 50% or higher), efficacy is lost due to immune response to the product. Immunogenicity may be stimulated by the presence of protein aggregates. In this project, we will use a hierarchical approach that uses advanced computer simulations combined with state-of-the art experiments to provide detailed, molecular-level information on the mechanisms by which protein aggregation occurs. Experiments will utilize synthetic proteins with designed chemical characteristics, model therapeutic proteins in murine models and commercial therapeutic proteins. Protein aggregates and pathways for their formation will be analyzed using a wide array of experimental techniques including single-molecule total internal reflectance fluorescence-Forster resonant energy transfer, small angle neutron scattering, small angle x-ray scattering micro-flow imaging, surface micro-rheology, chromatography, circular dichroism spectroscopy and infrared spectroscopy. A major focus of this renewal proposal will be the extension of our current work on protein aggregation in homogeneous solutions to protein aggregation that occurs due to interactions with interfaces such as those found in delivery devices (e.g., syringes, IV bags, IV lines, and delivery pumps).